By now the most difficult part of our task has been attempted, so that if the reel and spindle revolve “sweetly” in the bearings, no doubt need be entertained as to whether the motor will ever reach completion.
The bell-bobbin must be mounted with its magnet faces as near the reel circumference as possible, and with their centers the same height above the baseboard as the spindle. A piece of wood beneath the bobbin, of such thickness as to keep it at the right height, and another strip across the top, through the ends of both of which screws are driven into the baseboard, will secure the magnet firmly in position ([Fig. 18]). The next operation is to bend a springy strip of brass to the shape shown in F, [Fig. 19], and fix it immovably by the screw G—round which one free end of the bobbin wire (L) has been twisted several turns—to the baseboard, so that its top portion misses the metal square or contact-breaker (P) on the spindle by about 1⁄4 inch. Now drive a second screw (R) carefully into the wood through another hole in the strip, until this latter presses lightly against each point of the contact-breaker successively as the spindle revolves.
Fig. 19.—The contact-breaker.
Fig. 20.—Showing wire connections (X, Y, Z) and motor.
The little motor is now complete, except, perhaps, for the addition of two terminal screws, one of which is joined with the remaining free bobbin wire, and the other by a short length of wire to either of the bearings. The entire connections are shown in the accompanying sketch ([Fig. 20]). Now for working! Connect the battery wires to the motor terminals, and adjust the spindle so that one corner of the contact-breaker is fairly touching the vertical brass strip. A current should now be flowing round the bobbins, which consequently become magnetized and attract the nearest iron nail fastened to the thread reel. If the iron is not sufficiently near to be under the magnet’s influence, turn the reel on the shaft until it is in the proper position. The motor, with a little adjustment, ought to run merrily, as the bell-bobbin—alternately magnetized and demagnetized—attracts and releases the short iron bars.
Experiment 8.—Connect the battery terminals together by means of some thin iron wire such as is used for wiring flowers, and twist it into a spiral so that it may rest comfortably in a cup of cold water (A, [Fig. 21]). Stand also therein a thermometer (B, [Fig. 21]). The water’s temperature will be observed to rise steadily, showing that the passage of the electric current heats the iron wire (C, [Fig. 21]), which in turn imparts some warmth to the surrounding liquid.
Fig. 21.—Warming water by electricity.